Campaigners have lost the latest legal battle against possible expansion at Stansted Airport, bought by Manchester Airports Group for £1.5bn earlier this year.

A High Court judge rejected their accusation that the key criteria being applied to decide on potential options for new runway sites in England were "infected by apparent bias".

The Stop Stansted Expansion group (SSE) had asked Mrs Justice Patterson, sitting in London, to order the Government-appointed Airports Commission, which was set up last year to address the issue of aviation expansion in the UK, to delay the publication of any options shortlist until the criteria have been looked at again and consulted on.

SSE said there was apparent bias because of the conduct of Geoff Muirhead, a recently resigned member of the Commission.

The judge ruled that both Mr Muirhead and the Commission might have acted in a way that was not "the most wise" and their conduct could have been regarded by a fair-minded observer as "less than ideal". But the apparent bias accusation was not supported by the evidence.

The court heard that Manchester Airports Group (MAG), the owner of Stansted since February, submitted proposals to the Commission for a two-runway option at Stansted, and also a four-runway hub airport option which would make Stansted the largest airport in the world.

Aviation expert Mr Muirhead is a former chief executive of MAG. In September, he stepped down as one of the five commissioners appointed by the Commission after SSE warned Transport Secretary Patrick McLoughlin they would take legal action if he stayed.

SSE said he retired as MAG's chief executive after 22 years with the group but was then immediately reappointed as "a highly paid ambassador to MAG, a role he continued to fulfil even after he was appointed to the Airports Commission".

Today, Mrs Justice Patterson observed that a "fair minded and informed observer would not have regarded the actions of Mr Muirhead in remaining as a commissioner until September 20, or those of the Commission in retaining him, as the most wise."

But she ruled a "defensive strategy" was adopted so that, "although the conduct of both parties was less than ideal", a "fair-minded and informed observer" would not have been satisfied there was "a real possibility of bias".

Such decisions that were made at the time were "provisional only".

Dismissing the legal challenge, the judge ordered SSE to pay legal costs of up to £10,000.

The unsucessful application for judicial review was brought by Peter Sanders and Brian Ross, described as "long-standing and key" members of SSE, which wants to contain the development of the Essex airport "within sustainable limits".

They asked the High Court to order the Commission, chaired by Sir Howard Davies, "to revisit certain key decisions made by the Commission during the time that Mr Muirhead was involved".

In a statement after today's ruling, SSE said the judge was critical of the Commission for not being more transparent about Mr Muirhead's consultancy arrangements.

SSE said: "The point she was referring to was that neither Geoff Muirhead nor the Commission had made any formal declaration that he was still being paid £150,000 a year by MAG when he was appointed to the Commission."

The statement added: "Although SSE has achieved its principal objective in pursuing this legal challenge, namely the removal of Mr Muirhead from the Commission, SSE still has some concerns about the integrity of the process going forward.

"Some of SSE's concerns were addressed in the course of the legal proceedings as a result of confidential information disclosed by the Commission in witness statements and exhibits, including the minutes of internal meetings.

"Despite its public commitment to be open and transparent, the Airports Commission considers that it is not subject to the Freedom of Information Act. Therefore, much of the information released to SSE as a result of its legal proceedings could not otherwise have been obtained.

"Because there is so much at stake, and because the position is still not entirely satisfactory, SSE needs time to give proper consideration to the judge's 60-page ruling and to discuss it in detail with its legal advisers before deciding whether there are aspects of the judgment that need to be taken to the Court of Appeal."